Space is curved. And time is part of space. And space and time contract as you speed up. Moreover, nothing can go faster than light. Nothing gets out of a black hole. ""Acceleration and gravity [are] intimately related."" These and other counterintuitive properties of our (expanding) universe all emerged from Einstein's theories of special and general relativity. Their consequences reshaped the world of physics--and their complexity has given generations of popularizers plenty of work. The latest book to tackle Einstein's insights and their consequences is also one of the clearest and shortest yet. Parker (Search for a Supertheory, etc.), a longtime professor of physics at Idaho State University, explains Einstein's theories in nonmathematical language, along with their famous predictions, tests and implications. A particularly strong chapter (with a full complement of clean diagrams) addresses the theory and practice of time travel. Parker looks with a friendly eye at the private lives of Einstein and his physicist contemporaries (his first chapter covers ""Einstein as a Youth""). But he devotes more space to the life of the universe--to its initial big bang and to its probable, gradual end. Starting with the 1887 Michelson-Morley experiment (which proved the nonexistence of an invisible, omnipresent stuff called ether), Parker addresses the findings that moved Einstein to his discoveries. Later chapters outline relativity's successors in the march of theoretical physics, notably quantum theory and Heisenberg's principle of uncertainty, which Einstein himself refused to accept. Students and others looking for fascinating and painless introductions to this particular, well-traveled, but still-startling corner of the sciences will be happy with Parker as their guide. (Sept.)